What Is NAD+? What It Does in the Body and What Supplements Claim

NAD+ (nicotinamide adenine dinucleotide) is a coenzyme, a helper molecule that cells use to turn food into energy and that DNA-repair enzymes burn as fuel.^[1] The body builds it from forms of vitamin B3 and from the amino acid tryptophan,^[2] and reviews have long said levels fall with age,^[5] although a 2026 study of seven human cohorts found whole-blood levels stable.^[16] Supplements and IV clinics promise to reverse that fall, but the evidence that doing so improves health in people is inconclusive. A 2026 systematic review, drawing on 33 human studies, concluded that oral boosters reliably raise NAD-related molecules in blood, while effects on health measures were “often null or endpoint-specific.”^[7]

What does NAD stand for, and what is the difference between NAD+ and NADH?

NAD stands for nicotinamide adenine dinucleotide. The “nicotinamide” part is a form of vitamin B3, and “dinucleotide” means two nucleotide units joined together. Cells hold it in two forms: NAD+, the oxidized form, and NADH, the reduced form.^[2] The two are the same molecule before and after it has picked up electrons, and keeping the balance between them is critical for normal cell function.^[2] A related molecule, NADP, carries a phosphate group and does similar work.^[3]

What does NAD+ do in the body?

NAD+ has two broad jobs. In the first it works like a rechargeable shuttle and is not used up. In the second it is spent, then rebuilt.

That second job is why NAD+ draws so much interest in aging research. The enzymes that use it sit close to processes that wear down over a lifetime, so a shortage has an obvious theoretical cost. A plausible theory is a starting point, and the authors of a leading review note that much remains to be learned about how NAD+ affects human health and aging.^[1]

Where does the body get NAD+?

You do not need to swallow NAD+ to have it. Cells make it through three routes: one starts from the amino acid tryptophan, one from nicotinic acid, and the salvage pathway recycles nicotinamide and related molecules, including the nicotinamide released when enzymes use NAD+ up.^[2] Diet supplies the raw materials. Niacin, the name for vitamin B3, is found in milk, eggs, enriched breads and cereals, rice, fish, lean meats, legumes, peanuts and poultry.^[4]

The recommended intake for adults is 16 mg a day for men and 14 mg a day for women, higher in pregnancy and while breastfeeding.^[4] A true deficiency causes pellagra, with digestive problems, inflamed skin and poor mental function.^[4] The supplements sold today are a different proposition: they aim to push NAD+ above the level a normal diet supports.

Does NAD+ decline with age?

Not clearly, at least in blood. A 2023 review by endocrinologists and aging researchers states that NAD+ levels decrease throughout life and that this decline has been postulated to contribute to age-related disease.^[5] The word “postulated” matters. A 2019 trial report described the decline as shown in preclinical models, with sparse human data.^[6] Another review calls lower NAD+ a hallmark of aging while conceding that the underlying causes remain unclear.^[2]

A 2026 study tested the premise directly. Researchers measured whole-blood NAD+ across seven independent human cohorts and found it stable with age and across lifestyle programs, although it did respond to nicotinamide riboside. They said the result challenges the use of blood NAD+ as a marker of aging.^[16] Blood is not muscle or brain, so this leaves open what happens inside other tissues. Raising NAD+ improved metabolism, heart function and healthspan in model animals,^[5] and human trials exist to test whether any of that carries over.

What do NAD supplements claim, and what do the trials show?

The claims on labels and clinic pages usually concern energy, metabolism, muscle and aging. Human trials support only part of the chain. Pills raise NAD-related molecules in blood.^[7] Whether that changes how a person feels or functions is the unresolved part.

Clinic drips get their own caution. A pilot study of a six-hour NAD+ infusion measured what happened to it in the blood,^[11] and the 2026 review found no eligible outcome trial of IV or injected NAD+ for anti-aging or wellness.^[7] The difference between an infusion and a capsule is set out in NAD+ vs NMN. If tiredness on a GLP-1 is what brought you here, the common causes are in fatigue on a GLP-1, and they have little to do with NAD+.

Is NAD+ a peptide, and is it FDA-approved?

NAD+ is not a peptide. Peptides are chains of amino acids, and NAD+ is built from nucleotides. It turns up on peptide menus because clinics sell it beside them, a grouping explained in what is peptide therapy. The HHS policy announced on October 28, 2026 names six peptides, and NAD+ is not among them.^[14]

FDA’s list of substances nominated for 503A compounding, as updated May 14, 2026, places NAD and NADH in Category 1, the group still under evaluation.^[13] Being on that list is not an approval and says nothing about whether it works. Sellers and status are on our NAD+ profile.

Is NAD+ safe?

In short trials, oral NR and NMN were generally well tolerated over weeks to months.^[7] Long-term data are limited. Drips are less comfortable: in a 2026 retrospective review of records from a commercial clinic, people given IV NAD+ reported moderate to severe stomach symptoms, a faster heart rate and chest pressure during the infusion, which resolved when it ended.^[12]

Two broader cautions apply to vitamin B3 itself. Too much niacin can raise blood sugar and cause liver damage, peptic ulcers and skin rashes.^[4] And a 2024 study of cardiac patients linked high blood levels of two breakdown products of excess niacin, 2PY and 4PY, to a higher three-year risk of major cardiac events.^[15] That was an association in people who already had a heart condition, and it did not test NAD+ supplements, but it is a reason not to assume that more is harmless.